Method of communicating signals through space.



,334. Patelited Dec. I6

L. DE FOREST 8|. E. H. SMYTHE. METHOD OF COMMUNICATING SIGNALS THROUGH SPACE.

(Application filed Aug. 4, 1902.)

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UNITED I STATES PATENT OFFICE.

LEE DE FOREST, OF JERSEY CITY, NEW JERSEY, A

OF CHICAGO, ILLINOIS, ASSIGNORS OF AMERICA, A CORPORATION OF METHOD OF COMMUNICATING SIGNALS THROUGH SPACE.

SPECIFICATION forming part of Letters Patent No. 716,334,

Original application filed July 5, 1901 Serial No. 67,136.

To all whom it may concern:

Be it known that we, LEE DE FOREST, residing at Jersey City, in the county of Hudson and State of New Jersey, and EDWIN II.

SMYTHE, residing at Chicago, county of Cook, State of Illinois, citizens of the United States, have invented a new and useful Method of Communicating Signals Through Space, of which the following is a specification.

This invention relates to a method of communicating signals through space.

The object of-the invention is to provide a method of detecting free electromagnetic waves for communicating signals through space which is simple and efficient and whereby communication may be carried on at a practically unlimited rate of speed and wherein the range or distance through which signaling may be effected may be increased.

Other objects of the invention will appear more fully hereinafter.

The invention consists, substantially, in the method of operation hereinafter more fully set forth, as illustrated in the accompanying drawings, and finally pointed out in the appended claims.

In methods of space-signaling heretofore employed it has been customary to utilize free electromagnetic waves in such manner as to produce a decrease in resistance in a local circuit, in which local circuit is arranged a signal-receiving device. In the apparatus employed in carrying out such an operation a responsive device, known as a coherer, is

employed and which is placed in the local circuit and also in a ground or capacity connection of a receiving aerial conductor. The resistance of the coherer under normal conditions is sufficiently high to arrest or retard the 0 flow of current in the local circuit; but when excited by an electric impulse or oscillation the resistance of the coherer is decreased, thereby allowing an increased flow of current in the local circuit and the consequent actuation of the signal-receiving device included in such local circuit. The resistance of the coherer, however, continues low after the impulse which caused the decrease has ceased, and in order to restore the coherer to its normal high resistance and sensitive condition,

dated December 16, 1902.

Divided and this application filed August 4, 1902. Serial (No model.)

so that it may respond to another impulse, it

is necessary to subject the coherer to a mechanical shock,or, as itis termed, decohere it, this being usually effected by auxiliary apparatus provided for that purpose. A method of operation and apparatus of this nature is subject to the limitation that the speed of response of the receiving apparatus to successive electrical impulses or free electromagnetic waves must necessarily be limited by thelag of the decoherin g mechanism. Thus in practice the average speed attained by the coherer systems of wireless telegraphy probably does not exceed some ten or twelve words per minute, whereas in ordinary telegraphy an operator is able to send and receive at several times that rate. Moreover, the decohering mechanism is ordinarily electromagnetically actuated, and the sparks which occur when the circuit through this electromagnetic 7o mechanism is broken, as well as those generated at the contacts of the Morse relay and in the receiving-circuit proper, interfere with the proper operation of the coherer unless special means and precautions be used to prevent such disturbances.

It is among the special purposes of our invention to avoid the objections noted and to provide a method of operation whereby the rate of speed of operation of the receiving or responsive device is increased, and we accomplish these objects by causing the electromagnetic Waves to produce or build up resistance in the local circuit instead of decreasing or breaking down such resistance, as in the coherer systems, and our objects are further accomplished by varying or increasing the resistance in the local circuit uniformly and proportioned to the energy of the received or successive electromagnetic waves, said resisto ance being again decreased by the action of a local current. In other words, in carrying out our method we employ a local circuit including a source of current the efiect and action of which is to predetermine and nor- 5 mally maintain a n u mber of conducting-paths through the responsive device, which is also included in said local circuit, and which paths are ruptured or interrupted by the action of the oscillations generated by the reroo ceived impulses and in uniform and proportional relation to the energy of the oscillations, thereby building up the resistance of the responsive device, and when the influence of the oscillations ceases the local current instantly reestablishes or reconnects these conducting-paths. In this manner we secure an instant and automatic return to normal condition after each received impulse and without requiring the use of any auxiliary mechanical, electromagnetic, or other apparatus for restoring such normal condition. In other words, we employ a local circuit in which the resistance is normally low and also cause such resistance to rise during excitation and to fall again to its normal condition immediately upon cessation of the exciting impulse, such rise and fall of resistance in the local circuit being substantially uniform and proportioned to the energy of successive impulses. In this manner the responsive period is practically coextensive with the duration of the received oscillation. Consequently, no matter how rapidly within Wide limits the exciting impulses succeed one another, each is separately recorded in the signal-receiving device.

In the accompanying drawings we have disclosed forms of apparatus adapted for carrying our method into practical operation, and referring to such drawings' Figure 1 is a diagrammatic view of a receiving-circuit including a responsive device or receiver of a construction and arrangement adapting the same to the carrying out of the principles of our invention. Fig. 2 is a similar view showing a slightly-modified arrangement of apparatus adapted to the carrying out of our invention. Figs. 3, 4, and 5 show modified forms of receiving device adapted to the carrying out of our invention. Fig. 6 is an enlarged broken detail View of a modified form of apparatus of the construction shown in Fig. 4.

In systems wherein electrical oscillations are utilized for signaling through space it is customary to employ an aerial receiving-conductor adapted to be cut by electrical oscillations or free electromagnetic Waves sent out from a generating or transmitting apparatus. This aerial conductor is provided with a grounded or capacity connection, in which is placed a responsive device or receiver, this being also included in a local circuit which contains a source of current and a signal-receiving device or relay. To cause the electric oscillations generated in the aerial receiving-conductor as far as possible to traverse only the path of the local circuit containing the responsive device, self-induction or choke coils are included in that part of the local circuit which would otherwise shunt the responsive device with respect to the received oscillations.

We have illustrated an arrangement embodying these general features, wherein A designates the aerial receiving-conductor, G

the ground or capacity connection of said conductor, and E a responsive device. In the construction of this responsivedevice adapting it to the carrying out of theprinciples of our method said responsive device comprises, generally, electrodes 6' e separated from each other with an interposed medium a hereinafter to be more fully referred to.

B designates the local battery; 0 0, the self-induction or choke coils; R, a resistance which We have found convenient and desirable to include in the local circuitin order to reduce the current flowing therein; F; acondenser shunting the resistance, and TT the signal-receiving device; This signal-receiving device is represented in Fig. 1 as an ordinary telephone-receiver and in Fig.: 2 as a telegraph-sounder, in this instance being located in a local circuit with a battery B, said circuit being controlled by a relay H, included in the first-mentioned local circuit. It is obvious, however, that the signal-receiving device may be of any suitable construction or arrangement, so long as it is responsive to the changes in the current-flow governed by the responsive device E.

As shown in Fig. 1, the aerial receiving-conductor A is connected with the ground or capacity connection G by a conductor 1, which includes the electrodes 6' e and the interposed medium 6 of detector E in series therein. At a point intermediate conductor A and detector E a conductor 2 is connected with conductor 1, which conductor 2 is again united with conductor 1 at a point between detector E and ground or capacity connection G. This conductor 2 includes serially choke-coil O, signal-receiver T, resistance R, across the terminals of which isconnected condenser F, battery B, and choke-coil O and constitutes the local circuit.

The circuit connections in Fig. 2 are similar to those of Fig. 1 except that condenser F is omitted, and instead of receiver T being included in the local circuit of conductor 2 it is placed in a secondary circuit 3, which is controlled by a relay I-I, included in conductor 2 and arranged between choke-coil O and resistance R.

Referring now more particularly to the construction of responsive device, which, as shown, is adapted to the carrying out of our improved method, we have found that when two metallic electrodes are slightly separated and included in series in a circuit containing a source of current and a suitable medium is interposed in series between their opposed surfaces minute metallic particles are torn 0% from the anode under theinfluence of the local current traversing the circuit which includes said electrodes and interposed medium in series and which particles are carried across the gap separating the electrodes to the cathode, said metallic particles building up little trees and bridges, which extendout toward and some reaching the anode, thus bridging the gap. As long as these bridges continue between the electrodes the resistance of the device is comparatively low; but under the influence of an electric impulse or oscillation, such as results when a spark passes between the terminals of an inductioncoil, these metallic bridges between the electrodes are instantly disrupted, and the resistance in the gap, and consequentlyin the circuit which includes the gap, increases greatly. Ifa signal-receiving device be included in the local circuit with the detector, this variation or increase in resistance is made manifest as the passage of the impulse is signaled. Between each spark at the apparatus employed in the production or generation of the oscil-- lation or free electromagnetic wave these bridges between the electrodes are again built up, or rather on the cessation of the impulse or oscillation the metallic particles again form into chains across the gap, and so automatically restore the conductivity of the device.

In our first experiments we employed wa ter in the gap between the electrodes. While such an arrangement was operative, still the results were not entirely satisfactory, for while the device would continue sensitive to electric impulses for a short time it would soon cease to be responsive. In order to determine the cause of this action and in order to develop a method which would be reliable and permanent, we made a number of experiments and microscopical examinations. In the course of these we have found that when water is employed between the elec trodes the gap between said electrodes as the action above described proceeds becomes filled in a very short space of time with minute particles, the anode being eaten away and the cathode correspondingly built up by deposition, and that when the received impulses are weak the device soon ceases to respond to them. An actualadherence between the minute particles seems to occur and the electrical oscillations or impulses are unable to disrupt the bridges, the device thus becoming clogged or unsensitive. We have also found that the clogging eifect in the gap between the electrodes occurs more rapidly when the impulses are weak. In order to overcome this difficulty and to increase and maintain the sensitiveness of the apparatus, we have tried the effect of interposing a great many different media in the gap between the electrodes and have found a number which give satisfactory results. Among these are various viscous liquids, such as glycerin and heavy oils, viscous semisolids, as Vaseline, porous solids, non-conducting .or poorly-conducting powders, as sulfur and the oxids of lead, fibers and fabrics and combinations of the above, as fibers or fabrics saturated with glycerin, and a mixture of the oxid of lead, (PbO,) commonly known as litharge,and glycerin. Wehavealsousedcollodion and gelatin with very fair results. Such media apparently act to support the chains of metallic particles, to retain the particles in operative relation with the electrodes and with each other, to limit the number of chains between the electrodes, and to confine the energy of the received impulse to these sensitive connecting-links. WVe have found that by employing media of this nature in the gap between the exposed surfaces of the electrodes the bridges across the gap are built up in the manner as above explained, but the promiscuous filling of the gap by the metallic particles does not occur, and that when a comparatively few bridges have formed the current confines itself to them. When the electrical impulse passes, these bridges or chains instead of being badly and violently broken up or disrupted and the particles comprising them scattered broadcast such particles are retained and supported in the near vicinity of or in proximity to each other and at the cessation of the impulse rapidly re-form into their original bridging relation. If the medium interposed in the gap is non-conducting or of small conductivity, the opposed electrodes are in a manner insulated from each other except where the gap is bridged by the chains of conducting particles, and the energy of the oscillation or impulse is therefore probably more concentrated upon these chains. This tends to prevent the clogging of the device when the received impulses are weak and to make the action uniformly more sensitive and to prevent agglomeration of the conducting particles. In other words, the resistance of the device is increased under the influence of the received energy-waves. Such increase of resistance is uniform and is substantially proportioned to the strength or energy of the received Wave, and upon the cessation of the received energy-wave the normally low resistance condition is again and automatically restored by the re-forming of the particles in conducting-chains, as above explained.

In our microscopical investigations of the action occurring in the gap between the separated electrodes we have noticed that when the local current is flowing the passage of the received impulse or oscillation causes a sudden evolution of bubbles of gas at the cathode and among the metallic particles forming the chains which bridge the electrodes. It is apparently due to this sudden generation of gas among the metallic particles that the conducting-chains are disrupted, and it is our theory that the action in thedevice islargely one of disruptive electrolysis in a film or stratum of electrolytic or electrically-decomposable liquid which,we believe, lies between each metallic particle and its neighbor. To supply such a liquid, the presence of which, according to our theory, is necessary to the peculiar action which takes place as above described, we sometimes mix with the supporting medium interposed betweenthe electrodes a small amount of water or other suitable electrically-decomposable body. It is not always necessary to do this, however, as

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many of the media employed contain such a constituent either rightfully or as an impurityas, for instance, commercial glycerin. The presence of the gas which is thus evolved during the action appears to play some part in bringing about the clogged or non-sensitive condition of the device, the probable explanation being that after continuous action the minute particles forming the bridges become surrounded by a gaseous instead of by a liquid envelop, that when this occurs the electrical impulses effect an actual adherence between the particles instead of the normal disruptive action. At any rate we have found it desirable to provide some means for disposing of this gas and prevent its accumulation in the gap. In one case, where the liquid interposed between the electrodes was distilled water, it was observed that all the gas was given off at the cathode or at the secondary cathodes among the minute metallic particles bridging the gap. In accordance with the well-known laws of electrolysis this gas should be and probably is hydrogen. The oxygen liberated apparently enters into combination with the metal of the anode. When the media interposed between the electrodes is glycerin with a slight percentage of water mixed with it, the action is apparently the same,

except that in this case the chemical activity of the nascent oxygen may be sufficient to cause it to abstract hydrogen from the glycerin to form water. The hydrogen, however, is apt to accumulate and eventually interfere with the operation. We have found it desirable to provide against this undesirable result and that several agents are satisfactory for this purpose, among which are the oxids of lead, previously mentioned as serving well in the capacity of a supporting and retaining medium. We have also employed manganese dioxid and potassium chlorate, but thus far have obtained the best results with the oxids of lead. The action of these various substances or agents is apparently that of a depolarizer, and the operation when such an agent is employed would seem to indicate that depolarization or its equivalent is continuously carried on. This depolarizing medium may be interposed directly between the active surfaces of the electrodes along with the interposed supporting medium, or it may be merely brought into close proximity to the active surfaces of the electrodes, in which position, as we have discovered both microscopically and experimentally, it still exerts a depolarizing effect, or, if such depolarizing medium is of the proper nature, it may serve itself as a supporting medium to retain and support the metallic particles as well as performing the function of a depolarizer.

The removal of the electrolytic gas above referred to may also be effected by the use of an absorbent material,which may be supplied to the supporting medium or may itself be interposed between the electrodes, and thus serve in the double capacity of a supporting medium and an absorbent or depolarizer. Powdered sulfur and other inert solids in a state of fine division we have found produce good result as an absorbent as well as a supporting medium.

The electrodes which we employ with the various forms of responsive device adapted to the carrying out of our method are preferably about one-eighth of an inch in diameter. In the forms represented in Figs. 1 and 3 the opposed surfaces of the electrodes are preferably Hat and separated from each other by about two to five one-thousandths of an inch. In the forms represented in Figs. 2, 4, and 6 the opposed surfaces of the electrodes are preferably roughened and separated from each other by about one-sixteenth to oneeighth of an inch.

It is sometimes advantageous to make the exposed, opposed, or juxtaposed surface of one of the electrodes, preferably the negative one, as 6 Fig. 5, cup-shaped, as shown at 6 having a narrow edge surrounding the cup or-recess and opposed to the plane surface of the other electrode a The cup or recess is filled with a mass of lead oxid and glycerin to a point flush with the surface of the surrounding edge.

Provision may be made for changing the relative separation of the electrodes. This may be accomplished by screw-threading the stems of one or both of the electrodes, as shown at c, and tapping the same through the support on which said electrode is mounted.

We have found it advantageous to employ a number of sensitive elements in series with each other and in which our method may be carried into practical operation. An illustrative form of apparatus employing this idea is shown in Fig. 4:. This comprises an insulating-tube 70, into the ends of which the electrodes e 6 project, and one or more auxiliary pieces or electrodes 6 placed in said tube and between the electrodes 6 6 being separated from said electrodes by spaces of, say, from one-sixteenth to one-eighth of an inch. In these spaces we place a mixture of rather coarse metal filings and a powder, such as litharge, in about equal proportions by bulk. This mixture is made into a rather fluid paste by means of glycerin or Vaseline with a slight amount of an electrically-decomposable body, such as water or alcohol, added thereto.

If desired, the auxiliary electrode or piece e may be omitted, as shown in Fig. 6. In either case the effect of a series arrangement is secured, the metallic fragments or filings forming substantially auxiliary or secondary electrodes.

In Fig. 1 the medium a represented as in terposed between the electrodes e 6 may be glycerin, oil, or Vaseline containing a small amount of water or other electrically-decomposable body. The medium represented as interposed between the electrodes in Fig. 3 may be fiber or a fabric, as silk cloth, "saturated with, say, glycerin containing a small amount of water. The proportion of water which we have found convenient to mix with the glycerin when employed in the forms shown in Figs. 1 and 3 is about one'part to four or five of glycerin. In the forms shown in Figs. 4 and 6 the proportion of water or decomposable body desirable is considerably less.

The most satisfactory metals, both for the electrodes and for the conducting particles or fragments to be interposed between the electrodes, we have found to be tin, silver, and nickel, in the order named; but we do not desire to be limited to the use of any particular metals, as others may be found equally suitable.

The current employed in the local batterycircuit is preferably small-say from onetenth to one milliampere. WVhen we employ two cells of battery,we have fou nd it desirable to make the resistance of the local circuit from twelve thousand to fifteen thousand ohms.

To have found the most satisfactory electrolytes or decomposable bodies employed in connection with the interposed medium in carrying out our method to be water, commercial alcohol, and ammonia, or a mixture of these. It is obvious, however, that other bodies may be found equally satisfactory. We do not desire, therefore, to be limited in this respect. Commercial glycerin ordinarily contains water in sufficient amount to make it suitable for our purpose or, if desired, water or alcohol, or both, may be mixed with the glycerin.

In the foregoing description We have referred to the use of a condenser in shunt around the resistance placed in the local circuit. The function of this condenser is to prevent the sound in the receiving-signal device, if a telephone, from being muffled and to render the same sharp and clear. We have found this use of the condenser to be quite advantageous.

The method of detecting Hertz oscillations or free electromagnetic impluses, such as above described, enables us to secure an instantaneous response or indication of the passage of the electrical impulse or Wave and an instantaneous or automatic restoration to normal condition at the cessation of an impulse and without the necessity of employing auxiliary mechanical or electromagnetic apparatus for such purpose, and the successive variations in resistance due to the influence of the received energy Waves are comparatively uniform and substantially proportioned to the energy of said successive waves.

In carrying out our improved method when a telephone-receiver is employed the listening operator hears a distinct and separate click for every spark produced at the transmitting or generating station. If a long series of such sparks be made at the sending or transmitting instrument or station, the receiving operator hears a similar series of sounds or clicks in the telephone, which may represent a dash, for instance, of the Morse code. A short series of sparks at the transmitting or generating station may represent a dot of the Morse code, and hence the speed of transmission and receipt of the message are limited only by the ability of the operators to send and receive signals.

In the foregoing description we have referred to the use of metallic particles interposed between the electrodes. By the use of the word metallic, however, We do not desire to be limited to pure metal, as it may be possible that these particles are metal in chemical combination with other elementsas, for instance, oxygen.

We do not claim herein the construction or arrangement of apparatus employed in carrying out our invention and as disclosed herein, as the same is set forth, described, and claimed in our pending application, Serial No. 67,136, filed July 5, 1901.

Having now set forth the object and nature of our invention and various embodiments of apparatus adapted for carrying the same into practical operation, what we claim as new and useful and of our own invention, and desire to secure by Letters Patent, is-

1. The method of transmitting signals through space which consists in establishing electrical oscillations in predetermined paths, then causing such oscillations to rupture such paths more or less completely, and finally utilizing the resulting efiective increase of resistance to produce a sensible effect or indication, as and for the purpose set forth.

2. The method of transmitting signals through space which consists in establishing electrical oscillations in predetermined paths, then producing by such oscillations a series of interruptions in such paths, and finally utilizing the resulting variations in effective resistance due to such interruptions to produce sensible indications, as and for the purpose set forth.

3. The method which consists in establishing conducting-paths in a local circuit of comparatively low resistance, and then disrupting such paths under the influence of oscillations produced by the received energy-waves,as and for the purpose set forth.

4. The method which consists in maintaining electrical pressure in a local circuit, said pressure normally operating to decrease the resistance in said circuit, and then increasing such resistance under the influence of oscillations produced by the received energywaves, as and for the purpose set forth.

5. The method which consists in maintaining electrical pressure in a local circuit, said pressure normally operating to establish conducting-paths of comparatively low resistance, and then disrupting said conductingpaths under the influence of oscillations produced by the received energy-waves and in proportion to the energy of such waves to increase the resistance of said circuit, whereby on cessation of said Waves a normally low resistance condition is restored in said circuit, as and for the purpose set forth.

6. The method which consists in maintaining electrical pressure in a local circuit, said electrical pressure normally operating to close said circuit through comparatively low resistance and then increasing said resistance by the action of oscillations produced by the received energy-waves and in substantial proportion to the strength of the received energywaves, as and for the purpose set forth.

7. The method which consists in establishing conducting-paths of comparatively low resistance by the action of an electric current in a normally closed local circuit, and then impressing upon said conducting-paths electrical oscillations produced by the received energy-Waves, whereby said cond noting-paths are disrupted during the passage of the rel subscribing witnesses.

LEE DE FOREST. EDWIN H. SMYTHE.

\Vitnesses for Lee de Forest:

M. W. NOLAN, G. B. SHEPPARD.

Witnesses for Edwin H. Smythez' S. E. DARBY, CHAS. H. SEEM.

day of August, 1902, in the presence of the 30 

